FIG. 1 illustrates the configuration of a W-CDMA communication system as an example of a configuration of a mobile communication system which includes a conventional radio access network.
As illustrated in FIG. 1, radio access network (RAN) 10 of this conventional example is composed of radio network controllers (RNC) 40a, 40b, and Node B's 60a-60d. This RAN 10 is connected to core network (CN) 3, which is an exchange network, through a Iu interface. As an interface between Node B's 60a-60d and RNC's 40a, 40b, a Iub interface is defined, while a Iur interface is defined as an interface between RNC's 40a, 40b. Details on the configuration of FIG. 1 are described in the following document:
Document: 3GPP TS 25.401 V5.4.0 (2002-09) (3rd Generation Partnership Project: Technical Specification Group Radio Access Network: UTRAN Overall Description [Release 5])
Node B's 60a-60d are logical nodes for performing radio transmission and reception, and specifically, they are radio base stations. Each of Node B's 60a-60d covers one or a plurality of cells 100, and is connected to user equipment (UE) 2 through a radio interface to terminate a radio channel.
RNC's 40a, 40b manage Node B's 60a-60d, and also select and combine radio paths in the event of a soft handover. RNC's 40a, 40b each comprise a physical integration of a function of controlling a C-plane (Control Plane) which is a protocol for transferring control signals for signaling control to set and release a call, and a function of controlling a U-plane (User Plane) which is a protocol for transferring user data related to user equipment (UE) 2.
In a conventional radio access network in which the U-plane control function and C-plane control function are integrated, when one wishes to improve the signaling throughput, the entire RNC must be added though the C-plane control function alone should be added. When one wishes to improve a user data transfer rate, the entire RNC must be added although it should only be necessary to add just the U-plane control function. In this way, the configuration of the conventional RNC encounters difficulties in building a highly scalable system.
Therefore, there has recently been proposed in some fields, as a configuration of a radio access network, a configuration which physically separates a C-plane controller for controlling the C-plane, and a U-plane controller for controlling the U-plane as separate devices.
According to this configuration, a C-plane controller alone should be added when one wishes to improve the signaling throughput, while a U-plane controller alone should be added when one wishes to improve a user data transfer rate, thus making it possible to build a highly scalable system.
As specific configurations, a variety of configurations can be contemplated, including a configuration in which n U-plane controllers are arranged to belong to a single C-plane controller, a configuration in which m U-plane controllers are arranged to belong to n C-plane controllers, and so on. Further, in the configuration in which m U-plane controllers are arranged to belong to n C-plane controllers, one U-plane controller can be arranged subordinate to two or more C-plane controllers.
However, in a conventional radio access network in which a C-plane controller is physically separated from a U-plane controller, a problem arises in that extreme difficulties are experienced in the management of the status of the U-plane controller (particularly, the management of status information on continuously varying traffic and the like) which can be readily confirmed in an existing system configuration in which both U-plane and C-plane control functions are integrated with each other.
Particularly, in a configuration in which m U-plane controllers are arranged to belong to n C-plane controllers, and a single U-plane controller is arranged subordinate to two or more C-plane controllers, a C-plane controller is not aware how its subordinate U-plane controllers are used by other C-plane controllers, thus making it more difficult to manage the status of the U-plane controllers subordinate thereto.
In this way, in the radio access network in which the C-plane controller is physically separated from the U-plane controller, it is difficult to manage the status of the U-plane controller. For this reason, when the traffic varies from one minute to the next particularly in a handover operation which involves addition of a radio link and the like, resources of the U-plane controller cannot be allocated in an efficient manner. Therefore, a need exists for a certain control method which can accomplish the management of the status of the U-plane controller and the handover operation, which has been done in existing systems.
It is an object of the present invention to provide a radio access network control method, and a radio access network which are capable of accomplishing the management of the status of the U-plane controller and a handover operation in the radio access network, in which a C-plane controller is physically separated from the U-plane controller.